Multicomponent gas mixtures containing hydrogen as a bulk primary component, a bulk secondary component and one or more dilute components are frequently encountered in industrial separation. A typical and widely adopted commercial source for the production of hydrogen is by reforming of natural gas or other methane-rich hydrocarbon stream. The reforming is carried out by reacting the hydrocarbon with steam and/or with a molecular oxygen-containing gas (e.g. air or oxygen-enriched air), producing a hydrogen gas stream containing accompanying minor amounts of oxides of carbon, residual methane and in some instances also nitrogen. Unless it is desired to recover the carbon monoxide for a designed use, it is customarily converted to carbon dioxide by water gas shift reaction. Bulk removal of carbon dioxide from the crude hydrogen stream may be effected by selective absorption in a physical solvent such as aqueous ethanolamines or alkali metal carbonates. To obtain high purity hydrogen the remaining dilute components are then removed by any of a variety of methods known to the art, among which are included selective adsorption in a pressure swing system (PSA) employing as adsorbent molecular sieve, most commonly a commercially available type 5A sieve.